The space solar yacht Tiger Moth under the command of no-nonsense Captain Lisa Deranne is on a cruise taking some rich misfits on a voyage through space. Unfortunately on their travels they have picked a stowaway, a shape-changing Rutan, a race that has been at war with another race, the Sontarans, since the dawn of time. The Rutan has important news regarding the war and the Sontarans, and upon hearing the news, attack the Tiger Moth and take it over. The Rutan hides itself among the crew and one by one the Sontarans and the human crew are murdered by the Rutan. The Sontarans plan to destroy all life on the Tiger Moth. Can Lisa find out who the Rutan is before the Sontarans destroy her ship and her life?...